Our kids are just finishing 9th grade and I am wondering at what age should they take their first SAT/ACT ?? Is there an advantage to having them take it early?? how old do they have to be before they can take it??

The real key is the PSAT, taken in the junior year (age 16?). Top scores in the PSAT can get you National Merit scholarships and a lot of interest from top colleges, and since test prep statistically raises scores by some 30 points, it's good to get in some practice and maybe one exam before you do it for real. I think you can take the PSAT as a sophomore. Any time after you take the PSAT is fine for taking the SAT and/or ACT.